1. Field of the Invention
The present invention relates to a laminate type electronic component and a method for manufacturing the laminate type electronic component, and more particularly, relates to a laminate type electronic component including an external electrode formed directly by plating such that the external electrode is connected electrically to a plurality of internal electrodes, and a method for manufacturing the laminate type electronic component.
2. Description of the Related Art
Laminate type electronic components typified by laminated ceramic capacitors are, in general, provided with a component main body which has a stacked structure including, for example, a plurality of stacked functional material layers composed of a dielectric ceramic, and a plurality of layered internal electrodes formed along the interfaces between the functional material layers. The respective ends of the plurality of internal electrodes are exposed, for example, at each of first and second end surfaces of the component main body, and external electrodes are formed so as to electrically connect the respective ends of the internal electrodes to each other.
For the formation of the external electrodes, typically, a conductive paste including a metal constituent and a glass constituent is applied onto the end surfaces of the component main body, and then subjected to firing, thereby forming paste electrode layers first. The paste electrode layers serve to electrically connect the internal electrodes to each other. Next, a first plating layer containing, for example, nickel as its main constituent is formed on the paste electrode layers, and a second plating layer containing, for example, tin or gold as its main constituent is further formed thereon. The second plating layer is intended to ensure solderability, whereas the first plating layer serves to prevent solder erosion in the case of a solder joint.
As described above, the external electrode is typically composed of the three-layer structure of the paste electrode layer, the first plating layer, and the second plating layer.
However, the paste electrode layer described above has a large thickness of several tens μm to several hundreds μm. Therefore, in order to limit the dimensions of the laminate type electronic component up to certain specifications, there is undesirably a need to reduce the effective volume for ensuring a capacitance, because there is a need to ensure the volume for the paste electrode layers. On the other hand, the plating layers each have a thickness on the order of several μm. Thus, if the external electrodes can be composed only of plating layers, a larger effective volume can be ensured for ensuring the capacitance.
For example, Japanese Patent Application Laid-Open No. 63-169014 discloses depositing conductive metal films by electroless plating over the entire surfaces of sidewalls of a component main body, at which internal electrodes are exposed, so as to short-circuit the internal electrodes exposed at the sidewalls, and using the conductive metal films as external electrodes.
However, in the method for forming external electrodes as described in Japanese Patent Application Laid-Open No. 63-169014, the ends with the internal electrodes exposed are subjected to plating directly, and thus, the ingress of a plating solution into the component main body may occur along the interface between the internal electrodes and the insulator layers. In addition, the ingress of moisture other than the plating solution into the component main body may occur.
On the other hand, for the purpose of enhancing the fixing strength of the plating films to serve as external electrodes with the component main body, a heat treatment may be carried out at a temperature on the order of 800° C. or more after the plating step. In this case, commonly, the moisture in the component main body will be removed by evaporation with the aid of the heat treatment. However, the path for releasing moisture in the component main body is covered with the plating films after the plating step, thus not only interfering with the release of moisture, but also causing blisters or bulge defects in the plating films.